Can openers are well known. In general, they comprise a traction wheel and a cutting wheel. One wheel can be rotated and the traction wheel acts as a reaction surface and also acts to drive the can opener around the lip of the can while the sharpened cutting wheel cuts through the can. The most popular type of can opener available is the type that cuts the top lid of the can to gain access to the can contents. The main problem with this mode of opening is that the cutting blade cuts down through the lid and tends to come into contact with the contents of the can. This is a problem if the cutting blade is dirty from previous use. If the cutting blade is not particularly sharp, it will tend to form small metal shavings that fall into and contaminate the contents of the can. If the entire circumference of the can lid is cut, the top lid often falls into the can contents and can be difficult and messy to remove from the interior of the can.
To address these problems, can openers have been developed that are designed to cut the outside seam of the can. Examples of these can openers include U.S. Pat. No. 3,719,991 to French; U.S. Reissued Pat. No. 27,504 to Smith; U.S. Pat. No. 1,935,680 to Von Wolforsdorf; U.S. Pat. No. 4,782,594 to Porucznik et al. and U.S. Pat. No. 3,510,941 to Fyfe. All these patents disclose a can including a pin sliding in an arcuate slot for engaging and locking the can opener on the can to be opened. While these arrangements work adequately, over time there is a tendency for the moving parts to wear with the result that the engaging and locking function of the opener is impaired leading to difficulty in cutting the can and keeping the opener in position on the can.
My own U.S. Pat. No. 5,121,546, granted Jun. 16, 1992, discloses an effective solution of the above problem. In the can opener disclosed in that patent, there are thrust surfaces and a separating means that can be introduced between the thrust surfaces. The separating means, typically a ball bearing, is introduced between the thrust surfaces and moves a movable thrust surface away from a fixed thrust surface to separate a movable wheel, usually the traction wheel, and a cutting wheel. By this means, the can opener is brought to the cutting position. The wheel can then be rotated to cut the can. While the can opener disclosed in my U.S. Pat. No. 5,121,546 has proved to be extremely effective, experiments with groups of people have shown that a certain dexterity is required in order to effectively operate the can opener. Such dexterity is not always present because many persons opening cans do not have a great deal of dexterity.
My second U.S. Pat. No. 5,367,776, granted Nov. 29, 1994, discloses a can opener comprising a housing having a handle. The cutting wheel has a cutting edge for severing a can wall, the cutting wheel defining a cutting wheel axis. The opener also has a traction wheel having a gripping surface which engages a can, the traction wheel defining a traction wheel axis. The opener also includes means for rotatably mounting the traction wheel and the cutting wheel in the housing such that their axes are substantially perpendicular and the wheels are positioned adjacent and spaced apart from each other to define a gap to accept the seam of the can to be opened. One of the wheels is movable towards the other in order to engage and lock the can between the cutting wheel and the traction wheel so that the cutting wheel acts to sever the can wall. The traction wheel acts to move the can past the cutting wheel. A first thrust surface is associated with the housing and a spaced, adjacent, second thrust surface is associated with the moveable wheel. The first and second thrust surfaces comprise cooperable cam surfaces which are rotatable relative to each other to reciprocate the first and the second thrust surfaces relative to each other between a first position, where the gap is relatively wide, and a second position where the gap is narrow and the can is engaged and locked between the cutting wheel and the traction wheel. Means are associated with one of the wheels to permit rotation thereof.